clippy: Fix some warnings in script/dom (#31915)

* fixed some clippy warnings

* resolved conflict

* updated texttracklist.rs

---------

Co-authored-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/texttrack.rs

@@ -142,7 +142,7 @@ impl TextTrackMethods for TextTrack {
             // gecko calls RemoveCue when the given cue
             // has an associated track, but doesn't return
             // the error from it, so we wont either.
-            if let Err(_) = old_track.RemoveCue(cue) {
+            if old_track.RemoveCue(cue).is_err() {
                 warn!("Failed to remove cues for the added cue's text track");
             }
         }